The most dangerous time for heart attack patients are the days and weeks following their heart attack, and a new study shows that U.S. patients are readmitted within a month of being discharged from the hospital far more often than patients in other developed countries. It’s not that American patients aren’t treated properly, but that they might not be kept in the hospital long enough.

The study, published in the Journal of the American Medical Association (JAMA), looks at more than 5,500 patients who had a severe heart attack in which the coronary artery was completely blocked by a blood clot, a condition known as a STEMI (or an ST-segment elevation myocardial infarction). In the U.S., most STEMI patients in the study stayed no more than three days in the hospital after their heart attacks. But in the 16 other countries surveyed — Canada, Australia, New Zealand, and 13 European countries — most patients stayed about twice as long—at least six days.

And although the Americans got to go home much sooner than their foreign counterparts, they paid a price for their earlier discharge, landing back in hospital much more often.

Just under 10% of STEMI patients overseas needed readmission to the hospital within 30 days of discharge. In the U.S., 14.5% did. And readmission, according to the study researchers, can have implications for patient care. The infections and other complications that bring patients back can impede successful recovery from heart attacks.

“Readmission should be avoided if at all possible, everyone agrees on that,” senior study author Manesh Patel said in a written statement to reporters.

Patel added:

This [finding] speaks to how health care is provided in the United States. In the United States, care is episodic, not always coordinated, and it’s not clear in many cases whether the patient is seen again by the same doctor or care team within the first seven days after discharge. When they are discharged quickly, they are at risk for being readmitted because the system may not be in place to effectively manage them when issues arise.

The U.S.’s high readmission rate is also a problem for hospital administrators and health-care policy analysts. That’s because since 2009, the JAMA study reports, the U.S. Centers for Medicare & Medicaid Services has been using 30-day readmission rates from some key conditions — including acute myocardial infarction, or heart attacks — as a measure of hospital quality.

Hospitals want to keep costs low, so they have an incentive to send patients home as soon as they can leave. But it may hurt the hospitals’ quality ratings — and ultimately, perhaps, drive up total costs as well — if patients need additional care because they were sent home too soon.

Previous research has found wide variation in readmission rates across the U.S. In their JAMA article this week, Patel and co-authors write that this variation is considered a sign of “inconsistent quality of care” across the country. That’s a wake up call for re-assessing how we treat heart attacks in the U.S., and whether we need to give patients more time to recover properly before declaring them ready for discharge.